How each process forms the part
Die casting injects molten aluminum, zinc, or magnesium into a hardened steel die at high pressure, then ejects a near-net-shape part after the metal solidifies. It is a net-shape process: most of the final geometry, including thin walls, ribs, and bosses, is created in the tool.
CNC machining is subtractive. It starts from a solid billet, bar, or near-net casting and removes material with rotating cutters to reach the final geometry. Nothing is added; the parent material's properties are preserved because you are only shaping existing stock.
When die casting is the better choice
Choose die casting when you need thousands of identical metal parts with thin walls, complex ribs, and integrated features, and per-part cost must fall as volume rises. Consumer hardware, enclosures, brackets, and housings are classic fits.
Because the mold defines the shape, die casting delivers excellent repeatability and surface quality straight from the tool, with minimal secondary machining beyond drilled holes and threaded inserts. It is the volume champion for light, complex metal parts.
When CNC machining is the better choice
Choose CNC when the part is low-to-mid volume, still evolving, or must hold very tight tolerances and clean threads without draft angles. Machining also wins for high-strength wrought alloys that cannot be cast, and for parts where any porosity is unacceptable.
CNC is also the right call for bridge production and prototypes: you get a real metal part fast, with no mold lead time and no sunk tooling if the design changes. For one part or a few hundred, machining usually beats casting on both cost and speed.
Cost and the break-even point
Die casting carries a large fixed cost: the steel die can run from a few thousand to tens of thousands of dollars and takes weeks to build. But once it exists, each shot is cheap, so unit cost collapses as volume climbs into the thousands.
CNC has near-zero setup for a one-off and modest programming cost that spreads across the run. The crossover with die casting often sits in the low-to-mid thousands of pieces, depending on part size, alloy, and how much machining the casting would still need.
Tolerances, accuracy and materials
CNC holds about plus or minus 0.02 mm on metal and works any wrought or aerospace alloy, aluminum, steel, titanium, or brass, with full density and traceable stock. That makes it the choice for bearing seats, hydraulic faces, and precision assemblies.
Die casting is coarser, roughly plus or minus 0.1 mm as-cast, and limited to castable alloys such as ADC12, A380, or Zamak. Shrinkage and porosity are inherent, so critical dimensions are usually machined after casting anyway.
Surface finish and post-processing
Die-cast parts leave the die with a smooth, consistent skin and can be polished, plated, powder-coated, or painted directly. The main post work is trimming the parting line, removing gates and ejector marks, and adding threaded inserts.
CNC parts arrive near-spec and take bead blast, anodize, or brush finishes cleanly. The difference is that casting often needs secondary CNC to true up datums and holes, whereas a fully machined part may need no further cutting at all.
Lead time and iteration speed
Die casting's clock starts with tooling: design, steel, sampling, and correction can take six to twelve weeks before the first good part. That is fine when the design is frozen and the run is long.
CNC can deliver a first metal part in days and re-cut a revised version almost as fast. For development, bridge runs, and anything still changing, machining keeps the program moving while the casting tool is, or is not, justified.
Strength, porosity and end-use parts
CNC parts are isotropic and fully dense; the alloy's native strength is retained because you are shaping solid stock. That is why load-bearing, safety, and pressure-containing components are almost always machined.
Die castings are sound for most structural uses but carry a small, predictable porosity and a cast grain. For high-pressure or fatigue-critical parts, specify vacuum-assisted casting and plan post-machining of sealing faces, or stay with CNC.
Typical applications by industry
Automotive and e-mobility use die casting for housings, brackets, and increasingly large structural parts; CNC makes the fixtures, prototypes, and low-volume precision components alongside them.
Electronics, medical, and robotics lean on CNC for enclosures and mechanisms in low volume, and turn to die casting only when a part's annual volume clears the tooling threshold. The decision tracks annual demand, not just unit price.
A practical decision checklist
Ask: Will I make more than a few thousand a year? Is the alloy castable and the wall thin? Can I freeze the design long enough to amortize a die? If yes across the board, die casting wins.
If volume is lower, the design is moving, or you need tight tolerances and zero porosity, choose CNC. Many programs prototype in CNC, prove the part, then migrate to die casting once the business case supports the mold.
How FabProto supports both processes
FabProto machines CNC parts and partners for die casting, so you do not have to commit to a mold before the design is proven. We cut your prototypes and low-volume runs in metal, with the tolerances and finishes a production part demands.
When volume justifies tooling, we help scope the die, estimate the break-even quantity, and even produce CNC bridge parts during the mold build. That staged path protects your budget from sinking a die into a shape that still evolves.